Hi @kris-a559, welcome to the community!
I'm happy to help with your automation.
It appears you're looking to run the automation over particular rows, so your FILTER formula will need to instead be in the field below (the "Run the step for these rows" field). You would not need to wrap it in IF() either, as that field is only looking for the defined rows to run the action on.
Delete the formula from the field it's currently in (leave it blank), and in the "Run the step for these rows" field, enter your FILTER formula:
=FILTER(Onboarding_Plans, "Onboarding_Plans[name]=% AND Onboarding_Plans[dob]<=%", $[SYS_USER], "")
Hope that helps and provides some clarity! Let us know if you have any other questions.